A&A 455, 773-777 (2006)
DOI: 10.1051/0004-6361:20065177

A catalogue of quasars and active nuclei: 12th edition[*]

M.-P. Véron-Cetty - P. Véron

Observatoire de Haute Provence, CNRS, 04870 Saint-Michel l'Observatoire, France

Received 9 March 2006 / Accepted 13 April 2006

Aims. This catalogue is aimed at presenting a compilation of all known AGN in a compact and convenient form and we hope that it will be useful to all workers in this field.
Methods. Like the eleventh edition, it includes position and redshift as well as photometry (U, B, V) and 6 cm flux densities when available. We now give 20 cm rather than 11 cm flux densities.
Results. The present version contains 85 221 quasars, 1122 BL Lac objects and 21 737 active galaxies (including 9628 Seyfert 1s), almost doubling the number listed in the 11th edition. We also give a list of all known lensed and double quasars.

Key words: galaxies: quasars: general - galaxies: Seyfert - galaxies: BL Lacertae objects: general

1 Introduction

The first catalogue of quasars was published in 1971 by De Veny et al. It contained 202 objects. The number of known quasars has since steadily increased until the year 2000 (see Table 1). The release of both the 2dF catalogue (Croom et al. 2001, 2003) and the first part (Abazajian et al. 2003) of the "Sloan Digital Sky Survey'' (Fan et al. 1999) has dramatically increased the number of known quasars justifying the 10th and 11th editions of the present catalogue. The recent release of the last three installments of the SDSS (Abazajian et al. 2004, 2005; Adelman-McCarthy et al. 2006) which has again almost doubled the number of known quasars, made a new edition timely.

This edition contains quasars with measured redshift known to us prior to January 1st, 2006; as in the preceding editions, we do not give any information about absorption lines or X-ray properties. But we give the absolute magnitude[*] for each object and, when available, 20 and 6 cm flux densities.

This catalogue should not be used for any statistical analysis as it is not complete in any sense, except that it is, we hope, a complete survey of the literature.

2 Description of the catalogue

Table 1: Increase with time of the number of known QSOs, BL Lacs and Seyfert 1s.

We have arbitrarily defined a quasar as a starlike object, or an object with a starlike nucleus, with broad emission lines and brighter than absolute magnitude MB=-23. The quasars are listed in Table_QSO. A sample page is shown in Fig. 1. Clearly, some objects would move from Table_QSO to Table_AGN and vice versa if other values for q0 and the spectral index were used or if an accurate B apparent magnitude was available for all objects. The variability may have a similar effect, as well as the size of the diaphragm used for the measurement as the contribution of the underlying galaxy for low-z quasars may not be negligible.

\end{figure} Figure 1: Sample page of the QSO catalogue.
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In Table_BL, we list all confirmed, probable or possible BL Lac objects with or without a measured redshift, without consideration of their absolute magnitude. As better spectra are becoming available, broad emission lines have been detected in a number of objects formerly classified as BL Lac; they have usually been moved to Table_QSO (Véron-Cetty & Véron 2000b).

Table_AGN lists "active galaxies'': Seyfert 1s, Seyfert 2s and Liners fainter than MB=-23[*]. A number of galaxies with a nuclear H II region are also included (158), the reason being that they have been called AGN in the past and later reclassified; we consider it useful to keep track of these reclassifications to avoid further confusion.

Seyfert 1s have broad Balmer and other permitted lines; Seyfert 2s have Balmer and forbidden lines of the same width. Osterbrock (1977, 1981) has divided the Seyfert 1s into five subgroups: Seyfert 1.0, 1.2, 1.5, 1.8 and 1.9 on the basis of the appearance of the Balmer lines. Seyfert 1.0s are "typical'' members of the class, as described by Khachikian & Weedman (1971, 1974), while Seyfert 1.5s are objects intermediate between typical Seyfert 1s and Seyfert 2s, with an easily apparent narrow H$\beta$ profile superimposed on broad wings. The classes Seyfert 1.2 and 1.8 are used to describe objects with relatively weaker and stronger narrow H$\beta$ components, intermediate between Seyfert 1.0 and 1.5 and Seyfert 1.5 and 2 respectively. In Seyfert 1.9, although the broad H$\alpha$ emission is clearly seen, broad H$\beta$ cannot be detected with certainty by mere visual inspection of the spectra. We have adopted the more quantitative classification introduced by Winkler (1992):
S1.0      5.0 < R  
S1.2 2.0 < R < 5.0  
S1.5 0.33 < R < 2.0  
S1.8   $\phantom{<}$ R < 0.33 broad component visible
      in H$\alpha$ and H$\beta$
S1.9     broad component visible
      in H$\alpha$ but not in H$\beta$
S2     no broad component visible
Q2     type 2 QSO

where R is the ratio of the total H$\beta$ to the [OIII]$\lambda$5007 fluxes. Several objects have been found to show extreme spectral variability, changing from Seyfert 1.8 or 1.9 to Seyfert 1.0. In some cases these changes are consistent with changes of the reddening towards the BLR while, in others, they are probably due to real changes in ionizing flux (Goodrich 1989a, 1995; Tran et al. 1992b). In some Seyfert 2s, a broad Pa $\beta$ line has been detected, indicating the presence of a highly reddened broad line region (Goodrich et al. 1994); we call these objects S1i. A number of Seyfert 2s have, in polarized light, the spectra of Seyfert 1s (Antonucci & Miller 1985; Miller & Goodrich 1990; Tran et al. 1992a); we call them S1h. Typical full widths at half-maximum of the Balmer lines in Seyfert 1s lie in the range 2000-6000 km s-1; however, there is a group of active galactic nuclei with all the properties of Seyfert 1s, but with unusually narrow Balmer lines (Osterbrock & Pogge 1985; Goodrich 1989b); they are defined as having the broad component of the Balmer lines narrower than 2000 km s-1 FWHM (Osterbrock 1987); we call them S1n. Liners (as defined by Heckman 1980) are called S3. If broad Balmer lines are observed, they are called S3b; if these broad Balmer lines are only seen in polarized light, they are called S3h.

Seyfert 1 galaxies and QSOs, when viewed through the absorbing dusty torus have the same optical appearance; however, they differ either by their hard X-ray luminosity or, for radio loud objects, by their radio luminosity. It has become customary to call type 2 QSOs (or Q2) rather than Seyfert 2 the high luminosity narrow line objects. Treister et al. (2005) call type 2 QSOs narrow line objects with  $L_{0.5{-}10~{\rm keV}}>10^{42}$ erg s-1 (H0=70 km s-1 Mpc-1) or >1042.3 erg s-1 if H0=50 km s-1 Mpc-1, while Derry et al. (2003) have more conservatively defined QSO2s as having an intrinsic, hard (2-10 keV) X-ray luminosity larger than 1044.3 erg s-1. Véron-Cetty & Véron (2000b) have shown that narrow line objects with a 178 MHz radio luminosity $S_{\rm 178}>10^{36}$ erg s-1 Hz-1 are QSO2s rather than Seyfert 2s.

In Table_AGN, 6875 objects have no classification. Most of them were originally classified as QSOs but turned out to be fainter than MB=-23 and were therefore moved to this table.

Table_reject lists the objects which once were believed to be AGN and are now known to be either stars or normal galaxies.

Table_QSO contains 85 221 objects, Table_BL, 1122, Table_AGN, 21 737 and Table_reject, 141. The catalogue is believed to contain all known quasars, BL Lac objects and Seyfert 1s.

Table_QSO, Table_BL and Table_AGN give:

1) Columns 1 and 2. The most common name of the object. For the meaning and the sources of the designations see Hewitt & Burbidge (1987), Fernandez et al. (1983) and Kesteven & Bridle (1977). For the sources discovered by the ROSAT X-ray satellite, we have used the following acronyms: RXS for the sources appearing in the All-Sky Bright Source Catalogue (Voges et al. 1999), 1WGA for the sources published in the WGACAT catalogue (White et al. 1994) and RX for the others.

When the name is preceded by an *, the object has not been explicitly associated with a radio source.

2) Columns 3 to 10. The best available J2000 optical or radio coordinates. The J2000 positions have been converted from the B1950 positions using the matrix given by Aoki et al. (1983). An O or an R following the coordinates means that the position is either an optical or a radio position measured with an accuracy better than one arcsec. An A means that it is only an approximate position which may be wrong by several arc minutes. No reference is given for the source of the positions. The availability of the Digitized Sky Survey (DSS) allows quick measurements of the optical position of any object brighter than $\approx$19.5 mag. It has already been used to measure the position of several hundreds QSOs (Schneider et al. 1992; Bowen et al. 1994; Kirhakos et al. 1994; Véron-Cetty & Véron 1996b). Optical positions with an accuracy better than 2 $\hbox{$^{\prime\prime}$ }$ have also been measured for the 19 369 galaxies in the Zwicky catalogue (Falco et al. 1999) and for the 12 921 UGC galaxies (Cotton et al. 1999).

3) Columns 11 to 14. The 6 and 20 cm flux densities (in Jy) with references to the literature. When several measurements are available we took arbitrarily one of them. When a reference is given for the 6 cm flux density but the value of the flux density itself is left blank and there is an * in Col. 1, only an upper limit is available and this upper limit is not much greater than 1 mJy; in case there is no * in Col. 1, the reference refers to a detection but at a wavelength other than 6 cm.

The 20 cm flux densities have been taken mainly from the NRAO VLA Sky Survey (NVSS) (Condon et al. 1998) and the FIRST survey (Becker et al. 1995; White et al. 1997). The NVSS covers the sky north of $\delta$(J2000.0 $) =-40^{\circ}$. The catalog contains 1 814 748 discrete sources stronger than $S\sim 2.5$ mJy. The resolution was 45 $\hbox{$^{\prime\prime}$ }$ FWHM. The rms uncertainties in $\alpha$ and $\delta$ vary from $\le$1 $\hbox{$^{\prime\prime}$ }$ for the sources stronger than 15 mJy to 7 $\hbox{$^{\prime\prime}$ }$ at the survey limit. The FIRST survey was carried out with the VLA. It covers an area of 9033 deg2 to a sensitivity limit of $\sim$1 mJy. The catalog contains 811 118 sources. Source positions are good to better than 1 $\hbox{$^{\prime\prime}$ }$. The beam size was 5 $\hbox{$.\!\!^{\prime\prime}$ }$4. Identifications of FIRST radio sources with the 2001 version of the present catalogue were previously attempted by Wadadekar (2004) who found 775 coincidences.

4) Columns 15 and 16. The redshift as published. An * in front of the redshift means that it has been estimated from a low dispersion slitless spectrum and is of lesser accuracy or even plainly wrong as the emission lines may easily be misidentified. We have given only those values which are described as probable in the original sources and not the possible values.

5) Column 17. In this column an attempt has been made to classify the objects as S1, S1.0, S1.2, S1.5, S1.8, S1.9, S1i, S1h, S1n, S2, Q2, S3, S3b, S3h, S, S? or H2. Low redshift quasars are classified as S1 when a good spectrum shows that they are similar to Seyfert 1 galaxies.

In Table_BL, we find in this column:
         BL        for a confirmed BL Lac object.
  BL? for a probable BL Lac
  blank for a possible BL Lac.
  ? for a questionable BL Lac
  HP for a Highly Polarized object.

6) Columns 18 to 21. The V, B-V and U-B photoelectric or photographic magnitude and colours, when available (the survey of the literature for photographic colours may be incomplete) (an * in front of the magnitude indicates that the colours and the magnitude are photographic, while an R or an I indicates a red or an infrared magnitude). The column labelled "V'' gives the V magnitude when B-V is also given. When B-V is not given, this column usually gives the B magnitude, unless it is preceded by an R or an I. Maoz et al. (1993) have measured homogeneous V magnitudes for 354 QSOs with an accuracy of $\pm$0.1 mag; they have been included. For a few objects the O magnitude, measured on the blue Palomar Sky Survey plates, or the UK Science Research Council SRC-J Survey plates, believed to be accurate within $\pm$0.2 mag, has been extracted from the APS database (Pennington et al. 1993). For a number of objects we give the O magnitude, extracted from the USNO-A2 catalogue (Monet et al. 1996) or the Cambridge Automated Plate Measuring Machine (APM) catalogue (Irwin et al. 1994), recalibrated by E. Flesch (private communication); these magnitudes are flagged with an O. The O and Johnson B magnitudes are related by  $B-O=-(0.27\pm0.06)\times (B-V)$ (Evans 1989).

\end{figure} Figure 2: Correction to be applied to the absolute magnitude if H0=71 km s-1 Mpc-1, $\Omega _{\rm M}=0.29$ and $\Omega _{\Lambda }=0.71$ rather than H0=50 km s-1 Mpc-1 and q0=0.
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Table 2: Gravitationally lensed quasars. Column 1: name, Col. 2: short 1950 position, Col. 3: redshift of the quasar, Col. 4: redshift of the lens, Col. 5: separation in arcsec, Col. 6: references.

Table 3: Quasar pairs. Column 1: name, Col. 2: short 1950 position, Col. 3: redshift of the quasar, Col. 4: separation in arcsec, Col. 5: references (see Table 2).

For the SDSS objects we give V, B-V and U-B computed from u', g' and r' by the following equations (Fukugita et al. 1996):




In the other cases, the magnitude given is an estimate as found in the original publications. These magnitudes are generally quite inaccurate and inhomogeneous; they are most often  $m_{\rm pg}$ or B magnitudes instead of the Johnson V magnitude. Much care should be taken when using them for any purpose. Anyway, even when a photoelectric V magnitude is given, it is not very meaningful as most quasars are variable. On the other hand, the colours of quasars vary little, so the listed colours should be accurate. Again, it should be noted that some of the colours listed are photographic and, therefore, less accurate; moreover, in each catalogue of photoelectric measurements, the faintest objects measured are affected by relatively large errors; this too should not be overlooked. For bright galaxies in Table_AGN, when photoelectric UBV photometry is available, we have chosen the magnitudes and colours measured in the smallest possible diaphragm (preferentially 16 arcsec) as we are interested in the nucleus rather than in the galaxy itself.

7) Column 22. The absolute magnitude MB computed assuming H0=50 km s-1 Mpc-1, q0=0, and an optical spectral index $\alpha$ (defined as  $S\propto \nu^{-\alpha}$) equal to 0.3 (Francis et al. 1991), as follows:

\begin{displaymath}{M = m} + 5 - 5\times \log {D} - {k + \Delta m(z)}\end{displaymath}

where m is the B magnitude, $D = c/H_{0}\times A$, with A the photometric distance (Terrell 1977):


z is the redshift; $k=-2.5 \log(1+z)^{1-\alpha}$ is the k correction, $\Delta m(z)$ is a correction to k taking into account the fact that the spectrum of quasars is not strictly a power law of the form $S\propto \nu^{-\alpha}$, but is affected by emission lines and by the Ly $\alpha$ forest depleting the continuum to the blue of Ly $\alpha$. Assuming that the spectrum is a power law with $\alpha=0.3$ may not give the best possible estimate of the k correction (Wisotzki 2000). The R magnitudes have been transformed into the B system by using an average $\langle B-R\rangle=0.57$ and the I magnitudes by using $\langle B-I\rangle=1.1$ for low z QSOs. When the reference for the magnitude is Maoz et al. (1993), the magnitude is V and we have used $\langle B-V\rangle =0.40$.

In a more realistic flat cosmology with H0=71 km s-1 Mpc-1, $\Omega _{\rm M}=0.29$ and $\Omega _{\Lambda }=0.71$ (see for instance Perlmutter et al. 1999 or Riess et al. 2004), the computed absolute magnitude would be systematically smaller than in the standard model adopted in the present paper. The correction to add to the absolute magnitude given in this catalogue is given in Fig. 2.

8) The next three columns (23 to 25) give the reference for the finding chart, the photometry and the redshift respectively. In many cases, the last reference in Table_AGN is that of the classification of the object (as a Seyfert or otherwise); in these cases the redshift can usually be found in Palumbo et al. (1983).

9) The B1950 position (Cols. 26 to 32).

Since the discovery in 1979 by Walsh et al. of the first gravitationally lensed quasar, Q 0957+561, a number of such objects (69) and of physical pairs with separation less than 10'' (38) have been found. They are listed in Tables 2 and 3 respectively. Mortlock et al. (1999) have stressed the difficulty sometimes encountered in distinguishing lensed quasars from physical pairs.

This research has made use of the APS catalogue of POSS I database which is supported by the National Science Foundation, the National Aeronautics and Space Administration, and the University of Minnesota. We are very grateful to E. Flesch and F. Ochsenbein for checking and improving the catalogue and we thank R. Monella for having brought to our attention a number of errors and omissions in previous editions.



Copyright ESO 2006